The effect on albumin-adjusted ("corrected") calcium, which is what our
users look at, is more complicated than a simple 6% fall. For the first few
weeks of the change we were reporting about 20% of our adjusted Ca's below
the lower reference limit (2.20 mmol/l). The effect was proportional to the
albumin concentration, ie at 30 g/l there was a 0.08 mmol/l difference, but
at 50 g/l it was 0.16 mmol/l. This predominantly affected the ambulant GP
patients, rather than the hospital sickies.
I have recalculated the equation so that the adjusted Ca's are "right" for
the new CFAS value, and written an apologetic letter to all the GP users.
For interest the equations are:
Adj Ca = Ca + 0.016(42-albumin) OLD
Adj Ca = Ca + 0.012(52-albumin) NEW
Paul
On Tue, 28 Mar 2006 12:02:02 +0100, Wills Philip (Queen Elizabeth Hospital
NHS Trust) <[log in to unmask]> wrote:
>Early replies (many thanks) are indicating the same
>misgivings that we have, with the Roche Cfas Calcium
>change.Many good thoughts,especially regarding the one
>standard and water zero.Trouble is, in this day of
>regulation,CE marking,traceability etc. we are being asked
>(forced) to make a change the outcome of which we know not to
>be in the best interest of the patient.(No-one jumps off a
>cliff just because they're told to!) Try justifying an
>alternative to the assigned calibration value to CPA - not
>that easy in reality.It is one thing to arrive at that
>situation, quite another to retrain countless GPs into
>understanding that 2.07 mmol/L is no longer
>hypocalcaemia.Please keep those thoughts coming in and we can
>revisit Roche with the strength of feeling about this.
>Phil
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